At present, foamed urethanes, non-elastic crimped staple stuffing, and resin-like stuffing, hard stuffing, etc. obtained by bonding of non-elastic crimped staples are used as a cushioning material for furniture, bedding such as a bed, trains, and automobiles.
However, although foamed-crosslinking type urethanes have excellent durability as a cushioning material, they have inferior moisture and water permeability, and thermal storage property to exhibit possible humid feeling. Since the foamed-crosslinking type urethanes do not have thermoplasticity, they have difficulty in recycling, and they give significant damage to incinerators in case of incineration, and need high costs in elimination of poisonous gas. For this reason, the foamed-crosslinking type urethanes are often used for reclamation, but limitation of reclamation spot based on difficulty of stabilization of ground causes problems of the necessity for higher costs. Furthermore, although the foamed-crosslinking type urethanes have excellent workability, they may cause pollution problems with chemicals that have been used in a manufacturing process. Since fibers are not fixed with each other in thermoplastic polyester bonded stuffings, deformation of shape in use, movement of fibers, and wear-out of crimp, and problems of fall of bulkiness and elasticity will occur.
Examples include resin-like stuffing obtained by adhesion of polyester fibers with adhesives, for example, a resin-like stuffing using a rubber based adhesive as adhesives (for example, refer to Patent Documents 1, 2, and 3), and a stuffing using a crosslinking type urethanes as adhesives (for example, refer to Patent Document 4.) These cushioning materials have inferior durability, and do not exhibit thermoplasticity, nor have single composition. For these reasons, they may cause a problem of impossibility of recycling, and complicated workability, problems of pollution with chemicals used in a manufacturing process etc.
In examples (for example, refer to Patent Documents 5, and 6) that use polyester hard stuffings, since the fiber component of the thermally fusible fiber uses an amorphous brittle polymer, the hard stuffing has a problem that a brittle bonded part will be easily broken in use to result in poor durability of deformation and deterioration of elasticity.
Although a method of intermingling treatment (for example, refer to Patent Document 7) is proposed as an improving method, a problem of brittleness of the bonded part is not yet solved, resulting in a great problem of deterioration of elasticity. In addition, the method also has complicated workability, and furthermore has a problem of difficulty in deformation of the bonded part, leading to inferiority in soft cushioning property. For this reason, proposed is a cushioning material utilizing a thermally fusible fiber using a soft polyester elastomer having recoverability from deformation in a part to be bonded (for example, refer to Patent Document 8). A polyester elastomer, serving as an bonding component, used for this fiber structure, includes 50 to 80 mol % of terephthalic acid in an acid component of a hard segment, and includes 30 to 50% by weight, as a content, of a polyalkylene glycol as a soft segment, in order to obtain a lower melting point. The polyester elastomer includes, as other acid component, isophthalic acid etc. to increase amorphous property and to give a melting point not more than 180° C. and a lower melt viscosity, resulting in formation of excellent thermally bonded part and of an amoeba-like bonded part. However, since the polyester elastomer is a sheath-core type conjugated fiber using a polyethylene terephthalate in a core part thereof, it exhibits high repellency to cause a problem of difficulty in fitness along a human body. It also has a problem of higher costs caused by use of a compound spinning fiber and by necessity for process of melting bonding with reheating.
Although a thermoplastic olefin network structure used for civil engineering works is proposed (for example, refer to Patent Document 9), the structure has poor touch due to uneven surface thereof unlike cushions including thin fibers, and has inferior cushioning properties based on use of a linear olefin as a material. In addition, although a network structure using vinyl chloride is proposed for door mats etc., the structure exhibits easy deformation by compression and inferior recoverability. Furthermore, the structure produces poisonous hydrogen halides in combustion to prove to be unsuitable to cushioning materials.
As substitute of urethanes, also investigated is a cushioning material including a mixture of a polyolefin resin; and a vinyl acetate resin, a vinyl acetate ethylene copolymer, or a styrene styrene-butadiene rubber (for example, Patent Document 10). However, this cushioning material has problems of: less sinking as compared with urethanes; a high stress at 25% compression; a small stress difference between compressed state and decompressed state to give excessively high repellency; poor light resistance caused by mixing with other components; and heavy weight based on large specific gravity.
There has been proposed a three-dimensional random loop bonded structure obtained by forming random loops by curling treatment of continuous linear structure including a polyester thermoplastic elastic resin, and by making each loop mutually contact in a molten state to weld the majority of contacted parts. The above-described structure, however, generally has a specific gravity of not less than 1.3, and tends to be heavy, and also causes a problem of needing cautions, in manufacturing control and use, due to inferior chemical resistance. In addition, since polyester thermoplastic resins have a benzene ring in a principal chain thereof, they have comparatively inferior light resistance; they may cause a problem of deterioration of elastic recoverability, in the case of use in environment exposed to sunlight, for a long period of time. And, since excessively larger recoverability exhibits excessively stronger repulsive force, in structures that use a polyester thermoplastic resin, the above-described structures give deformation along with human body, but they exhibit a large pressure difference between a portion with sufficient sink, and a portion with less sink, causing a problem of fatigue with long-time use. Furthermore, when a glass transition temperature is set in a lower temperature side by variation of a copolymerization ratio of polyester thermoplastic resins, softness will be increased, but conversely elastic recoverability significantly deteriorates, causing a problem of failure of fulfilling the function as a cushioning material.
Patent Document 1: Japanese Patent Publication No. S60-11352 A
Patent Document 2: Japanese Patent Publication No. S61-141388 A
Patent Document 3: Japanese Patent Publication No. S61-141391 A
Patent Document 4: Japanese Patent Publication No. S61-137732 A
Patent Document 5: Japanese Patent Publication No. S58-136828 A
Patent Document 6: Japanese Patent Publication No. H03-249213 A
Patent Document 7: Japanese Patent Publication No. H04-245965 A
Patent-Document 8: WO 91/19032
Patent Document 9: Japanese Patent Publication No. S47-44839 A
Patent Document 10: Japanese Patent Publication No. 2003-250667 A